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Stability, Formation and Dissociation Kinetics of the Pentacoordinate Ni 2+ and CO 2+ Complexes with 1,5‐Diazacyclooctane‐N,N′‐diacetic Acid
Author(s) -
Chatterjee Chinmay,
Kaden Thomas A.
Publication year - 1975
Publication title -
helvetica chimica acta
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.74
H-Index - 82
eISSN - 1522-2675
pISSN - 0018-019X
DOI - 10.1002/hlca.19750580703
Subject(s) - chemistry , dissociation (chemistry) , kinetics , aqueous solution , conjugate acid , reaction rate constant , conjugate , medicinal chemistry , limiting , acid dissociation constant , inorganic chemistry , ion , organic chemistry , mechanical engineering , mathematical analysis , physics , mathematics , quantum mechanics , engineering
The stability constants of the Ni 2+ and Co 2+ complexes with 1,5‐diazacyclooctane‐N,N′‐diacetic acid (H 2 DACODA) have been determined potentiometrically in 0.5 M KNO 3 at 25°. Only M(DACODA) and M(DACODA)OH − were observed. In addition the formation and dissociation kinetics of the pentacoordinate complexes M(DACODA) has been studied in aqueous solution using a stopped‐flow technique. Formation follows the rate law v f = k f [M 2+ ] [HDACODA − ]/[H + ], which can be interpreted as a bimolecular process either between M 2+ and DACODA 2− (k M,L ML ) or between MOH + and HDACODA − (k MOH,HL ML ). The second order rate constants k M,L MLare much higher than those expected from water exchange and can only be explained by a strong internal conjugate base effect. In the limiting case, however, this is equivalent to the second possible explanation, which assumes MOH + and HDACODA − as reactive species. The dissociation rate is given by v d = ( k ML + k H ML[H + ]) · [M(DACODA)].